Mimosine arrests cells in G1 by enhancing the levels of p27(Kip1)

The location and development of Replicon Cluster Domains in early replicating DNA

Background: It has been known for many years that in metazoan cells, replication origins are organised into clusters where origins within each cluster fire near-synchronously. Despite clusters being a fundamental organising principle of metazoan DNA replication, the genomic location of origin clusters has not been documented. Methods: We synchronised human U2OS by thymidine block and release followed by L-mimosine block and release to create a population of cells progressing into S phase with a high degree of synchrony. At different times after release into S phase, cells were pulsed with EdU; the EdU-labelled DNA was then pulled down, sequenced and mapped onto the human genome. Results: The early replicating DNA showed features at a range of scales. Wavelet analysis showed that the major feature of the early replicating DNA was at a size of 500 kb, consistent with clusters of replication origins. Over the first two hours of S phase, these Replicon Cluster Domains broadened in width, consistent with their being enlarged by the progression of replication forks at their outer boundaries. The total replication signal associated with each Replicon Cluster Domain varied considerably, and this variation was reproducible and conserved over time. We provide evidence that this variability in replication signal was at least in part caused by Replicon Cluster Domains being activated at different times in different cells in the population. We also provide evidence that adjacent clusters had a statistical preference for being activated in sequence across a group, consistent with the 'domino' model of replication focus activation order observed by microscopy. Conclusions: We show that early replicating DNA is organised into Replicon Cluster Domains that behave as expected of replicon clusters observed by DNA fibre analysis. The coordinated activation of different Replicon Cluster Domains can generate the replication timing programme by which the genome is duplicated.

Strengths and Weaknesses of Cell Synchronization Protocols Based on Inhibition of DNA Synthesis

Synchronous cell populations are commonly used for the analysis of various aspects of cellular metabolism at specific stages of the cell cycle. Cell synchronization at a chosen cell cycle stage is most frequently achieved by inhibition of specific metabolic pathway(s). In this respect, various protocols have been developed to synchronize cells in particular cell cycle stages. In this review, we provide an overview of the protocols for cell synchronization of mammalian cells based on the inhibition of synthesis of DNA building blocks-deoxynucleotides and/or inhibition of DNA synthesis. The mechanism of action, examples of their use, and advantages and disadvantages are described with the aim of providing a guide for the selection of suitable protocol for different studied situations.

Prognostic associations of plasma hepcidin in women with early breast cancer

PURPOSE

Iron is essential to energy metabolism, cell proliferation and DNA synthesis, and sufficient iron availability may be required for tumor growth. The hormone hepcidin is a systemic regulator of iron concentration in plasma. Intra-tumor RNA expression of hepcidin has been linked to shorter metastasis-free survival in women with early breast cancer, but the prognostic implications of this inflammatory marker and iron-regulating plasma peptide in the blood are unknown.

METHODS

Using an ELISA assay, hepcidin was measured in the banked blood of 518 women who were recruited from 1989 to 1996 for a prospective cohort study of diet and lifestyle factors in breast cancer. Blood samples were obtained 4-12 weeks post-operatively, prior to treatment with chemotherapy or tamoxifen.

RESULTS

Hepcidin was not associated with time to distant breast cancer recurrence (primary outcome) nor time to death from any cause. However, a pre-planned interaction test of body mass index (BMI) was statistically significant (p < 0.01). Among obese women (BMI > 30 kg/m²), higher hepcidin was associated with a shorter time to distant breast cancer recurrence in both uni- and multivariable analyses (adjusted HR 1.84; 95% CI 1.04-3.25). For overall survival, a similar pattern was seen in the univariable model but the effect was diminished in a multivariable analysis. Plasma hepcidin was not associated with high-sensitivity C-reactive protein, but it was significantly associated (r ≥ 0.32) with iron indices, including total iron (p < 0.01), transferrin (p < 0.01) and soluble transferrin receptor (p < 0.01).

CONCLUSIONS

Hepcidin may be associated with poor breast cancer outcome in obese women, however, replication is required. The biologic basis for this prognostic association requires further research.

Effects of P27/Bmdacapo, in the CIP/KIP family, on cell proliferation, growth and development in the silkworm (Bombyx mori)

We investigated changes in expression of the CIP/KIP family-related genes and the cycle-dependent factors Pcna, Cdk4 and Cdk2 during the growth and development of mice, Drosophila and silkworms. When the organism was in a period of rapid development, the related genes of the CIP/KIP family had low expression level and the cell cycle-dependent genes were highly expressed. In mammals, the CIP/KIP family includes three genes, p21, p27/Dacapo and p57. However, only one gene, P27/Dacapo, exists in the CIP/KIP family in silkworm and the orthologous gene in the silkworm is named Bmdacapo. Down-regulation of Bmdacapo in silkworm embryos caused overdevelopment of the embryos and indicated that Bmdacapo can inhibit silkworm growth and development. Up-regulation of Bmdacapo in silkworm cells inhibited cell proliferation, whereas down-regulation of Bmdacapo promoted cell proliferation. In order to explore the mechanism of Bmdacapo regulated silkworm development and cell proliferation, the effect of Bmdacapo on cell cycle changes was examined. The results demonstrate that Bmdacapo was able to induce G1/S phase arrest in the cell cycle. In silkworm cells, Bmdacapo inhibits the expression of Pcna, CDK4 and CDK2, which affects the cell cycle and ultimately inhibits cell proliferation. This regulatory mechanism is particularly different from mammals.

Oestrogenic activity of mimosine on MCF-7 breast cancer cell line through the ERα-mediated pathway

Hormone replacement therapy has been a conventional treatment for postmenopausal symptoms in women. However, it has potential risks of breast and endometrial cancers. The aim of this study was to evaluate the oestrogenicity of a plant-based compound, mimosine, in MCF-7 cells by in silico model. Cell viability and proliferation, ERα-SRC1 coactivator activity and expression of specific ERα-dependent marker TFF1 and PGR genes were evaluated. Binding modes of 17β-oestradiol and mimosine at the ERα ligand binding domain were compared using docking and molecular dynamics simulation experiments followed by binding interaction free energy calculation with molecular mechanics/Poisson-Boltzmann surface area. Mimosine showed increased cellular viability (64,450 cells/ml) at 0.1 μM with significant cell proliferation (120.5%) compared to 17β-oestradiol (135.2%). ER antagonist tamoxifen significantly reduced proliferative activity mediated by mimosine (49.9%). Mimosine at 1 μM showed the highest ERα binding activity through increased SRC1 recruitment at 186.9%. It expressed TFF1 (11.1-fold at 0.1 μM) and PGR (13.9-fold at 0.01 μM) genes. ERα-mimosine binding energy was -49.9 kJ/mol, and it interacted with Thr347, Gly521 and His524 of ERα-LBD. The results suggested that mimosine has oestrogenic activity.

Arabidopsis replication factor C4 is critical for DNA replication during the mitotic cell cycle

Replication factor C (RFC) is a conserved eukaryotic complex consisting of RFC1/2/3/4/5. It plays important roles in DNA replication and the cell cycle in yeast and fruit fly. However, it is not very clear how RFC subunits function in higher plants, except for the Arabidopsis (At) subunits AtRFC1 and AtRFC3. In this study, we investigated the functions of AtRFC4 and found that loss of function of AtRFC4 led to an early sporophyte lethality that initiated as early as the elongated zygote stage, all defective embryos arrested at the two- to four-cell embryo proper stage, and the endosperm possessed six to eight free nuclei. Complementation of rfc4-1/+ with AtRFC4 expression driven through the embryo-specific DD45pro and ABI3pro or the endosperm-specific FIS2pro could not completely restore the defective embryo or endosperm, whereas a combination of these three promoters in rfc4-1/+ enabled the aborted ovules to develop into viable seeds. This suggests that AtRFC4 functions simultaneously in endosperm and embryo and that the proliferation of endosperm is critical for embryo maturation. Assays of DNA content in rfc4-1/+ verified that DNA replication was disrupted in endosperm and embryo, resulting in blocked mitosis. Moreover, we observed a decreased proportion of late S-phase and M-phase cells in the rfc4-1/-^{FIS2;DD45;ABI3pro::AtRFC4} seedlings, suggesting that incomplete DNA replication triggered cell cycle arrest in cells of the root apical meristem. Therefore, we conclude that AtRFC4 is a crucial gene for DNA replication.

CKS protein overexpression renders tumors susceptible to a chemotherapeutic strategy that protects normal tissues

The cyclin-dependent kinase-interacting proteins Cyclin-dependent Kinase Subunit 1 and 2 (CKS1 and 2) are frequently overexpressed in cancer and linked to increased aggressiveness and poor prognoses. We previously showed that CKS protein overexpression overrides the replication stress checkpoint activated by oncoproteins. Since CKS overexpression and oncoprotein activation/overexpression are often observed in the same tumors, we have hypothesized that CKS-mediated checkpoint override could enhance the ability of premalignant cells experiencing oncoprotein-induced replication stress to expand. This tumor advantage, however, could represent a vulnerability to exploit therapeutically. Here, we first show in vitro that CKS protein overexpression selectively sensitizes tumor-derived cell lines to nucleoside analog-mediated toxicity under replication stress conditions. A treatment combination of the nucleoside analog gemcitabine and an agent that induces replication stress (thymidine or methotrexate) resulted in selective targeting of CKS protein-overexpressing tumor-derived cells while protecting proliferative cells with low CKS protein levels from gemcitabine toxicity. We validated this strategy in vivo and observed that Cks2-overexpressing mammary tumors in nude mice were selectively sensitized to gemcitabine under conditions of methotrexate-induced replication stress. These results suggest that high CKS expression might be useful as a biomarker to identify subgroups of cancer patients who might benefit from the described therapeutic approach.

Nucleoporins redistribute inside the nucleus after cell cycle arrest induced by histone deacetylases inhibition

Nucleoporins are the main components of the nuclear-pore complex (NPC) and were initially considered as mere structural elements embedded in the nuclear envelope, being responsible for nucleocytoplasmic transport. Nevertheless, several recent scientific reports have revealed that some nucleoporins participate in nuclear processes such as transcription, replication, DNA repair and chromosome segregation. Thus, the interaction of NPCs with chromatin could modulate the distribution of chromosome territories relying on the epigenetic state of DNA. In particular, the nuclear basket proteins Tpr and Nup153, and the FG-nucleoporin Nup98 seem to play key roles in all these novel functions. In this work, histone deacetylase inhibitors (HDACi) were used to induce a hyperacetylated state of chromatin and the behavior of the mentioned nucleoporins was studied. Our results show that, after HDACi treatment, Tpr, Nup153 and Nup98 are translocated from the nuclear pore toward the interior of the cell nucleus, accumulating as intranuclear nucleoporin clusters. These transitory structures are highly dynamic, and are mainly present in the population of cells arrested at the G0/G1 phase of the cell cycle. Our results indicate that the redistribution of these nucleoporins from the nuclear envelope to the nuclear interior may be implicated in the early events of cell cycle initialization, particularly during the G1 phase transition.

Neutrophil interactions with epithelial-expressed ICAM-1 enhances intestinal mucosal wound healing

A characteristic feature of gastrointestinal tract inflammatory disorders, such as inflammatory bowel disease, is polymorphonuclear neutrophil (PMN) transepithelial migration (TEM) and accumulation in the gut lumen. PMN accumulation within the intestinal mucosa contributes to tissue injury. Although epithelial infiltration by large numbers of PMNs results in mucosal injury, we found that PMN interactions with luminal epithelial membrane receptors may also play a role in wound healing. Intercellular adhesion molecule-1 (ICAM-1) is a PMN ligand that is upregulated on apical surfaces of intestinal epithelial cells under inflammatory conditions. In our study, increased expression of ICAM-1 resulted in enhanced PMN binding to the apical epithelium, which was associated with reduced PMN apoptosis. Following TEM, PMN adhesion to ICAM-1 resulted in activation of Akt and β-catenin signaling, increased epithelial-cell proliferation, and wound healing. Such responses were ICAM-1 dependent as engagement of epithelial ICAM-1 by antibody-mediated cross-linking yielded similar results. Furthermore, using an in-vivo biopsy-based, colonic-mucosal-injury model, we demonstrated epithelial ICAM-1 has an important role in activation of epithelial Akt and β-catenin signaling and wound healing. These findings suggest that post-migrated PMNs within the intestinal lumen can regulate epithelial homeostasis, thereby identifying ICAM-1 as a potential therapeutic target for promoting mucosal wound healing.

Inhibition of MCP-1 and MIP-2 Chemokines in Murine Trichinellosis: Effect of the Anti-Inflammatory Compound L-Mimosine

Mimosine, is a plant amino-acid which has been reported to block DNA replication in mammalian cells and to arrest cells reversibly towards the end of the G1 phase or at the beginning of the S phase. In this study, 42 mice were infected with T. spiralis, a nematode parasite, and treated with the anti-inflammatory compound L-mimosine, to determine if any alteration in the chronic inflammatory state occurred, by investigating the host's immunological response. MCP-1, a C-C chemokine and MIP-2, a C-X-C chemokine were tested and measured in the sera of infected animals, after 1, 10, 20, 30, 40, 50 and 60 days postinfection, by ELISA method. The diaphragm/muscle and the masseters of the infected mice, were tested for inflammatory response. We found that MCP-1 was partially inhibited by L-mimosine, while MIP-2 was totally inhibited. Moreover, in sections of the diaphragm and masseters, the infiltration of inflammatory cells such as macrophages, lymphocytes and eosinophils were more intense in untreated animals compared to those treated with L-mimosine. These findings show, that L-mimosine may have an inhibitory effect on MCP-1 and MIP-2 serum levels in Trichinellosis and may influence the recruitment of inflammatory cells and the intensity of the inflammatory reaction in this parasitic disease.

Inhibitory effect of l-mimosine on bleomycin-induced pulmonary fibrosis in rats: Role of eIF3a and p27

It has also been shown that the decreased expression of eukaryotic translation initiation factor 3a (eIF3a) by L-mimosine caused cell cycle arrest. Our previous study has found that eIF3a is involved in bleomycin-induced pulmonary fibrosis. Whether the eIF3a/p27 signal pathway is involved in the inhibitory effect of L-mimosine on bleomycin-induced pulmonary fibrosis remains unknown. Pulmonary fibrosis was induced by intratracheal instillation of bleomycin (5 mg/kg) in rats. Primary pulmonary fibroblasts were cultured to investigate the proliferation by BrdU incorporation method and flow cytometry. The expression of eIF3a, p27, α-SMA, collagen I and collagen III was analyzed by qPCR and Western blot. In vivo, L-mimosine treatment significantly ameliorated the bleomycin-mediated histological fibrosis alterations and blocked collagen deposition concomitantly with reversing bleomycin-induced expression up-regulation of eIF3a, α-SMA, collagen I and collagen III (both mRNA and protein) and expression down- regulation of p27. In vitro, L-mimosine remarkably attenuated proliferation of pulmonary fibroblasts and expression of α-SMA, collagen I and collagen III induced by TGF-β1, and this inhibitory effect of L-mimosine was accompanied by inhibiting eIF3a expression and increasing p27 expression. Knockdown of eIF3a gene expression reversed TGF-β1-induced proliferation of fibroblasts, down-regulation of p27 expression and up-regulation of α-SMA, collagen I, and collagen III expression. These results suggest that L-mimosine inhibited the progression of bleomycin-induced pulmonary fibrosis in rats via the eIF3a/p27 pathway.

Using Novel Method to Detect Different Cancer-Cell Stages of Model Human Lung Carcinoma

BACKGROUND

Synchrotron radiation infrared (SR-IR) microspectroscopy and SR-IR spectroscopic imaging are extremely valuable techniques for determining the molecular composition of biological and biomedical samples. In this work, SR-IR is applied in the study of the lung cancer cells in different cell cycles.

METHODS

We use a novel synchrotron based radiation infrared system combined synchronized model human lung carcinoma to reveal its unique character pattern.

RESULTS

After using SR-IR microspectroscopy, we discovered that the ratio of protein to lipid in G1 and G2 states is around 4.0 and 6.1, respectively. Moreover, for the DNA at the wavenumber position of 1225 cm(-1) , the intensity ratio of G2 state to G1 state is approximately 1.6. These data indicate that the cell in G1 state has more lipid composition to prepare for the DNA synthesis, but the cell in G2 state has more protein composition to prepare for the mitosis. The cell has larger DNA concentration in G2 state, which can be explained for the DNA synthesis.

CONCLUSION

Through our research, we demonstrate that different growth state of cancer cell presenting unique functional groups concentration profiles and distribution via using SR-IR microspectrometry. These applications will provide another ways to improve modern cancer screening in the future.

Expanding horizons in iron chelation and the treatment of cancer: role of iron in the regulation of ER stress and the epithelial-mesenchymal transition

Cancer is a major public health issue and, despite recent advances, effective clinical management remains elusive due to intra-tumoural heterogeneity and therapeutic resistance. Iron is a trace element integral to a multitude of metabolic processes, including DNA synthesis and energy transduction. Due to their generally heightened proliferative potential, cancer cells have a greater metabolic demand for iron than normal cells. As such, iron metabolism represents an important "Achilles' heel" for cancer that can be targeted by ligands that bind and sequester intracellular iron. Indeed, novel thiosemicarbazone chelators that act by a "double punch" mechanism to both bind intracellular iron and promote redox cycling reactions demonstrate marked potency and selectivity in vitro and in vivo against a range of tumours. The general mechanisms by which iron chelators selectively target tumour cells through the sequestration of intracellular iron fall into the following categories: (1) inhibition of cellular iron uptake/promotion of iron mobilisation; (2) inhibition of ribonucleotide reductase, the rate-limiting, iron-containing enzyme for DNA synthesis; (3) induction of cell cycle arrest; (4) promotion of localised and cytotoxic reactive oxygen species production by copper and iron complexes of thiosemicarbazones (e.g., Triapine(®) and Dp44mT); and (5) induction of metastasis and tumour suppressors (e.g., NDRG1 and p53, respectively). Emerging evidence indicates that chelators can further undermine the cancer phenotype via inhibiting the epithelial-mesenchymal transition that is critical for metastasis and by modulating ER stress. This review explores the "expanding horizons" for iron chelators in selectively targeting cancer cells.

The involvement of acidic nucleoplasmic DNA-binding protein (And-1) in the regulation of prereplicative complex (pre-RC) assembly in human cells

DNA replication in all eukaryotes starts with the process of loading the replicative helicase MCM2-7 onto chromatin during late mitosis of the cell cycle. MCM2-7 is a key component of the prereplicative complex (pre-RC), which is loaded onto chromatin by the concerted action of origin recognition complex, Cdc6, and Cdt1. Here, we demonstrate that And-1 is assembled onto chromatin in late mitosis and early G(1) phase before the assembly of pre-RC in human cells. And-1 forms complexes with MCM2-7 to facilitate the assembly of MCM2-7 onto chromatin at replication origins in late mitosis and G(1) phase. We also present data to show that depletion of And-1 significantly reduces the interaction between Cdt1 and MCM7 in G(1) phase cells. Thus, human And-1 facilitates loading of the MCM2-7 helicase onto chromatin during the assembly of pre-RC.

L-Mimosine blocks cell proliferation via upregulation of B-cell translocation gene 2 and N-myc downstream regulated gene 1 in prostate carcinoma cells

L-Mimosine, an iron chelator and a prolyl 4-hydroxylase inhibitor, blocks many cancer cells at the late G1 phase. B-cell translocation gene 2 (Btg2) regulates the G1/S transition phases of the cell cycle. N-myc downstream regulated gene 1 (Ndrg1) is a differentiation-inducing gene upregulated by hypoxia. We evaluated the molecular mechanisms of L-mimosine on cell cycle modulation in PC-3 and LNCaP prostate carcinoma cells. The effect of L-mimosine on cell proliferation of prostate carcinoma cells was determined by the [3H]thymidine incorporation and flow cytometry assays. L-Mimosine arrested the cell cycle at the G1 phase in PC-3 cells and at the S phase in LNCaP cells, thus attenuating cell proliferation. Immunoblot assays indicated that hypoxia and L-mimosine stabilized hypoxia-inducible factor-1α (HIF-1α) and induced Btg2 and Ndrg1 protein expression, but downregulated protein levels of cyclin A in both PC-3 and LNCaP cells. L-Mimosine treatment decreased cyclin D1 protein in PC-3 cells, but not in LNCaP cells. Dimethyloxalylglycine, a pan-prolyl hydroxylase inhibitor, also induced Btg2 and Ndrg1 protein expression in LNCaP cells. The transient gene expression assay revealed that L-mimosine treatment or cotransfection with HIF-1α expression vector enhanced the promoter activities of Btg2 and Ndrg1 genes. Knockdown of HIF-1α attenuated the increasing protein levels of both Btg2 and Ndrg1 by hypoxia or L-mimosine in LNCaP cells. Our results indicated that hypoxia and L-mimosine modulated Btg2 and Ndrg1 at the transcriptional level, which is dependent on HIF-1α. L-Mimosine enhanced expression of Btg2 and Ndrg1, which attenuated cell proliferation of the PC-3 and LNCaP prostate carcinoma cells.

Dentin matrix protein 1 induces membrane expression of VE-cadherin on endothelial cells and inhibits VEGF-induced angiogenesis by blocking VEGFR-2 phosphorylation

Dentin matrix protein 1 (DMP1) is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family, a group of proteins initially described as mineralized extracellular matrices components. More recently, SIBLINGs have been implicated in several key steps of cancer progression, including angiogenesis. Although proangiogenic activities have been demonstrated for 2 SIBLINGs, the role of DMP1 in angiogenesis has not yet been addressed. We demonstrate that this extracellular matrix protein induced the expression of vascular endothelial cadherin (VE-cadherin), a key regulator of intercellular junctions and contact inhibition of growth of endothelial cells that is also known to modulate vascular endothelial growth factor receptor 2 (VEGFR-2) activity, the major high-affinity receptor for VEGF. DMP1 induced VE-cadherin and p27(Kip1) expression followed by cell-cycle arrest in human umbilical vein endothelial cells (HUVECs) in a CD44-dependent manner. VEGF-induced proliferation, migration, and tubulogenesis responses were specifically blocked on DMP1 pretreatment of HUVECs. Indeed, after VE-cadherin induction, DMP1 inhibited VEGFR-2 phosphorylation and Src-mediated signaling. However, DMP1 did not interfere with basic fibroblast growth factor-induced angiogenesis. In vivo, DMP1 significantly reduced laser-induced choroidal neovascularization lesions and tumor-associated angiogenesis. These data enable us to put DMP1 on the angiogenic chessboard for the first time and to identify this protein as a new specific inhibitor of VEGF-induced angiogenesis.

Development of quantitative and high-throughput assays of polyomavirus and papillomavirus DNA replication

Polyoma- and papillomaviruses genome replication is initiated by the binding of large T antigen (LT) and of E1 and E2, respectively, at the viral origin (ori). Replication of an ori-containing plasmid occurs in cells transiently expressing these viral proteins and is typically quantified by Southern blotting or PCR. To facilitate the study of SV40 and HPV31 DNA replication, we developed cellular assays in which transient replication of the ori-plasmid is quantified using a firefly luciferase gene located in cis to the ori. Under optimized conditions, replication of the SV40 and HPV31 ori-plasmids resulted in a 50- and 150-fold increase in firefly luciferase levels, respectively. These results were validated using replication-defective mutants of LT, E1 and E2 and with inhibitors of DNA replication and cell-cycle progression. These quantitative and high-throughput assays should greatly facilitate the study of SV40 and HPV31 DNA replication and the identification of small-molecule inhibitors of this process.

Inhibition of HIV-1 gene expression by Ciclopirox and Deferiprone, drugs that prevent hypusination of eukaryotic initiation factor 5A

BACKGROUND

Eukaryotic translation initiation factor eIF5A has been implicated in HIV-1 replication. This protein contains the apparently unique amino acid hypusine that is formed by the post-translational modification of a lysine residue catalyzed by deoxyhypusine synthase and deoxyhypusine hydroxylase (DOHH). DOHH activity is inhibited by two clinically used drugs, the topical fungicide ciclopirox and the systemic medicinal iron chelator deferiprone. Deferiprone has been reported to inhibit HIV-1 replication in tissue culture.

RESULTS

Ciclopirox and deferiprone blocked HIV-1 replication in PBMCs. To examine the underlying mechanisms, we investigated the action of the drugs on eIF5A modification and HIV-1 gene expression in model systems. At early times after drug exposure, both drugs inhibited substrate binding to DOHH and prevented the formation of mature eIF5A. Viral gene expression from HIV-1 molecular clones was suppressed at the RNA level independently of all viral genes. The inhibition was specific for the viral promoter and occurred at the level of HIV-1 transcription initiation. Partial knockdown of eIF5A-1 by siRNA led to inhibition of HIV-1 gene expression that was non-additive with drug action. These data support the importance of eIF5A and hypusine formation in HIV-1 gene expression.

CONCLUSION

At clinically relevant concentrations, two widely used drugs blocked HIV-1 replication ex vivo. They specifically inhibited expression from the HIV-1 promoter at the level of transcription initiation. Both drugs interfered with the hydroxylation step in the hypusine modification of eIF5A. These results have profound implications for the potential therapeutic use of these drugs as antiretrovirals and for the development of optimized analogs.

Association of luteinizing hormone receptor gene expression with cell cycle progression in granulosa cells

During hormonally induced ovarian follicle growth, granulosa cell proliferation increases and returns to baseline prior to the administration of an ovulatory stimulus. Several key genes appear to follow a similar pattern, including the luteinizing hormone receptor (LHCGR), suggesting an association between cell cycle progression and gene expression. The expression of LHCGR mRNA in granulosa cells isolated from immature rats and treated in culture with FSH increased in a time-dependent manner, whereas administration of the cell cycle inhibitor mimosine completely suppressed expression. Although forskolin was able to induce luteinization in cells treated with mimosine, human chorionic gonadotropin had no effect, indicating the functional loss of LHCGR. The effects of mimosine on cell cycle progression and LHCGR mRNA expression were reversible within 24 h of mimosine removal. Cell cycle inhibition did not alter the stability of LHCGR mRNA, indicating that the primary effect was at the transcriptional level. To determine whether the relationship between LHCGR expression and cell cycle were relevant in vivo, immature rats were given a bolus of PMSG, followed by a second injection of either saline or PMSG 24 h later to augment levels of proliferation. The expression of LHCGR mRNA was elevated in the ovaries of animals receiving a supplement of PMSG. Mimosine also blocked cell cycle progression and LHCGR mRNA expression in macaque granulosa cells isolated following controlled ovarian stimulation cycles and in two different mouse Leydig tumor lines. These data collectively indicate that LHCGR mRNA is expressed as a function of the passage of cells across the G1-S phase boundary.

The promotion of human mesenchymal stem cell proliferation by superparamagnetic iron oxide nanoparticles

Superparamagnetic iron oxide (SPIO) nanoparticles are very useful in cell imaging; meanwhile, however, biosafety concerns associated with their use, especially on therapeutic stem cells, have arisen. Most studies of biosafety issues focus on whether the nanoparticles have deleterious effects. Here, we report that Ferucarbotran, an ionic SPIO, is not toxic to human mesenchymal stem cells (hMSCs) under the conditions of these experiments but instead increases cell growth. Ferucarbotran-promoted cell growth is due to its ability to diminish intracellular H2O2 through intrinsic peroxidase-like activity. Also, Ferucarbotran can accelerate cell cycle progression, which may be mediated by the free iron (Fe) released from lysosomal degradation and involves the alteration of Fe on the expression of the protein regulators of the cell cycle.

The interaction of the SRA domain of ICBP90 with a novel domain of DNMT1 is involved in the regulation of VEGF gene expression

Inverted CCAAT box-binding protein of 90 kDa (ICBP90) is over-expressed in several types of cancer, including breast, prostate and lung cancers. In search for proteins that interact with the set and ring-associated (SRA) domain of ICBP90, we used the two-hybrid system and screened a placental cDNA library. Several clones coding for a new domain of DNMT1 were found. The interaction, between the ICBP90 SRA domain and the DNMT1 domain, has been confirmed with purified proteins by glutathione-S-transferase pull-down experiments. We checked whether ICBP90 and DNMT1 are present in the same macro-molecular complexes in Jurkat cells and immortalized human vascular smooth muscle cells (HVTs-SM1). Co-immunoprecipitation experiments showed that ICBP90 and DNMT1 are present in the same molecular complex, which was further confirmed by co-localization experiments as assessed by immunocytochemistry. Downregulation of ICBP90 and DNMT1 decreased VEGF gene expression, a major pro-angiogenic factor, whereas those of p16(INK4A) gene and RB1 gene were significantly enhanced. Together, these results indicate that DNMT1 and ICBP90 are involved in VEGF gene expression, possibly via an interaction of the SRA domain of ICBP90 with a novel domain of DNMT1 and an upregulation of p16(INK4A). They further suggest a new role of ICBP90 in the relationship between histone ubiquitination and DNA methylation in the context of tumoral angiogenesis and tumour suppressor genes silencing.

Nanosecond electric pulses penetrate the nucleus and enhance speckle formation

Nanosecond electric pulses generate nanopores in the interior membranes of cells and modulate cellular functions. Here, we used confocal microscopy and flow cytometry to observe Smith antigen antibody (Y12) binding to nuclear speckles, known as small nuclear ribonucleoprotein particles (snRNPs) or intrachromatin granule clusters (IGCs), in Jurkat cells following one or five 10ns, 150kV/cm pulses. Using confocal microscopy and flow cytometry, we observed changes in nuclear speckle labeling that suggested a disruption of pre-messenger RNA splicing mechanisms. Pulse exposure increased the nuclear speckled substructures by approximately 2.5-fold above basal levels while the propidium iodide (PI) uptake in pulsed cells was unchanged. The resulting nuclear speckle changes were also cell cycle dependent. These findings suggest that 10ns pulses directly influenced nuclear processes, such as the changes in the nuclear RNA-protein complexes.

Enhanced replication of human T-cell leukemia virus type 1 in T cells from transgenic rats expressing human CRM1 that is regulated in a natural manner

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). To develop a better animal model for the investigation of HTLV-1 infection, we established a transgenic (Tg) rat carrying the human CRM1 (hCRM1) gene, which encodes a viral RNA transporter that is a species-specific restriction factor. At first we found that CRM1 expression is elaborately regulated through a pathway involving protein kinase C during lymphocyte activation, initially by posttranscriptional and subsequently by transcriptional mechanisms. This fact led us to use an hCRM1-containing bacterial artificial chromosome clone, which would harbor the entire regulatory and coding regions of the CRM1 gene. The Tg rats expressed hCRM1 protein in a manner similar to expression of intrinsic rat CRM1 in various organs. HTLV-1-infected T-cell lines derived from these Tg rats produced 100- to 10,000-fold more HTLV-1 than did T cells from wild-type rats, and the absolute levels of HTLV-1 were similar to those produced by human T cells. We also observed enhancement of the dissemination of HTLV-1 to the thymus in the Tg rats after intraperitoneal inoculation, although the proviral loads were low in both wild-type and Tg rats. These results support the essential role of hCRM1 in proper HTLV-1 replication and suggest the importance of this Tg rat as an animal model for HTLV-1.

Cell cycle progression and de novo centriole assembly after centrosomal removal in untransformed human cells

How centrosome removal or perturbations of centrosomal proteins leads to G1 arrest in untransformed mammalian cells has been a mystery. We use microsurgery and laser ablation to remove the centrosome from two types of normal human cells. First, we find that the cells assemble centrioles de novo after centrosome removal; thus, this phenomenon is not restricted to transformed cells. Second, normal cells can progress through G1 in its entirety without centrioles. Therefore, the centrosome is not a necessary, integral part of the mechanisms that drive the cell cycle through G1 into S phase. Third, we provide evidence that centrosome loss is, functionally, a stress that can act additively with other stresses to arrest cells in G1 in a p38-dependent fashion.

A gas-inducible expression system in HEK.EBNA cells applied to controlled proliferation studies by expression of p27(Kip1)

We describe an efficient inducible gene expression system in HEK.EBNA cells, a well-established cell system for the rapid transient expression of research-tool proteins. The transgene control system of choice is the novel acetaldehyde-inducible regulation (AIR) technology, which has been shown to modulate transgene levels following exposure of cells to acetaldehyde. For application in HEK.EBNA cells, AlcR transactivator plasmids were constructed and co-expressed with the secreted alkaline phosphatase (SEAP) gene under the control of a chimeric mammalian promoter (P(AIR)) for acetaldehyde-regulated expression. Several highly inducible transactivator cell lines were established. Adjustable transgene induction by gaseous acetaldehyde led to high induction levels and tight repression in transient expression trials and in stably transfected HEK.EBNA cell lines. Thus, the AIR technology can be used for inducible expression of any desired recombinant protein in HEK.EBNA cells. A possible application for inducible gene expression is a controlled proliferation strategy. Clonal HEK.EBNA cell lines, expressing the fungal transactivator protein AlcR, were engineered for gas-adjustable expression of the cell-cycle regulator p27(Kip1). We show that expression of p27(Kip1) via transient or stable transfection led to a G1-phase specific growth arrest of HEK.EBNA cells. Furthermore, production pools engineered for gas-adjustable expression of p27(Kip1) and constitutive expression of SEAP showed enhanced productive capacity.

A limited screen for protein interactions reveals new roles for protein phosphatase 1 in cell cycle control and apoptosis

Protein phosphatase 1 (PP1) catalytic subunits typically combine with other proteins that modulate their activity, direct them to distinct substrates, or serve as substrates for PP1. More than 50 PP1-interacting proteins (PIPs) have been identified so far. Given there are approximately 10 000 phosphoproteins in mammals, many PIPs remain to be discovered. We have used arrays containing 100 carefully selected antibodies to identify novel PIPs that are important in cell proliferation and cell survival in murine fetal lung epithelial cells and human A549 lung cancer cells. The antibody arrays identified 31 potential novel PIPs and 11 of 17 well-known PIPs included as controls, suggesting a sensitivity of at least 65%. A majority of the interactions between PP1 and putative PIPs were isoform- or cell type-specific. We confirmed by co-immunoprecipitation that 9 of these proteins associate with PP1: APAF-1, Bax, E-cadherin, HSP-70, Id2, p19Skp1, p53, PCNA, and PTEN. We examined two of these interactions in greater detail in A549 cells. Exposure to nicotine enhanced association of PP1 with Bax (and Bad), but also induced inhibitory phosphorylation of PP1. In addition to p19Skp1, PP1alpha antibodies also coprecipitated cullin 1, suggesting that PP1alpha is associated with the SCF1 complex. This interaction was only detectable during the G1/S transition and S phase. Forced loss of PP1 function decreased the levels of p27Kip1, a well-known SCF1 substrate, suggesting that PP1 may rescue proteins from ubiquitin/proteasome-mediated destruction. Both of these novel interactions are consistent with PP1 facilitating cell cycle arrest and/or apoptosis.

G1/S cell cycle arrest provides anoikis resistance through Erk-mediated Bim suppression

Proper attachment to the extracellular matrix is essential for cell survival. Detachment from the extracellular matrix results in an apoptotic process termed anoikis. Anoikis induction in MCF-10A mammary epithelial cells is due not only to loss of survival signals following integrin disengagement, but also to consequent downregulation of epidermal growth factor (EGFR) and loss of EGFR-induced survival signals. Here we demonstrate that G(1)/S arrest by overexpression of the cyclin-dependent kinase inhibitors p16(INK4a), p21(Cip1), or p27(Kip1) or by treatment with mimosine or aphidicolin confers anoikis resistance in MCF-10A cells. G(1)/S arrest-mediated anoikis resistance involves suppression of the BH3-only protein Bim. Furthermore, in G(1)/S-arrested cells, Erk phosphorylation is maintained in suspension and is necessary for Bim suppression. Following G(1)/S arrest, known proteins upstream of Erk, including Raf and Mek, are not activated. However, retained Erk activation under conditions in which Raf and Mek activation is lost is observed, suggesting that G(1)/S arrest acts at the level of Erk dephosphorylation. Thus, anoikis resistance by G(1)/S arrest is mediated by a mechanism involving Bim suppression through maintenance of Erk activation. These results provide a novel link between cell cycle arrest and survival, and this mechanism could contribute to the survival of nonreplicating, dormant tumor cells that avert apoptosis during early stages of metastasis.

Modulation of differentiation-related gene 1 expression by cell cycle blocker mimosine, revealed by proteomic analysis

L-mimosine, a plant amino acid, can reversibly block mammalian cells at late G1 phase and has been found to affect translation of mRNAs of the cyclin-dependent kinase inhibitor p27, eIF3a (eIF3 p170), and ribonucleotide reductase M2. The effect of mimosine on the expression of these genes may be essential for the G1 phase arrest. To determine additional genes that may be early respondents to the mimosine treatment, we performed two-dimensional gel electrophoretic analysis of [35S]methionine-labeled cell lysates followed by identification of the altered protein spots by LC-tandem mass spectrometry. In this study, the synthesis of two protein spots (MIP42 and MIP17) was found to be enhanced by mimosine, whereas the formation of another protein spot (MSP17) was severely blocked following mimosine treatment. These protein spots, MIP42, MIP17, and MSP17, were identified to be differentiation-related gene 1 (Drg-1; also called RTP, cap43, rit42, Ndrg-1, and PROXY-1), deoxyhypusine-containing eIF5A intermediate, and mature hypusine-containing eIF5A, respectively. The effect of mimosine on eIF5A maturation was due to inhibition of deoxyhypusine hydroxylase, the enzyme catalyzing the final step of hypusine biosynthesis in eIF5A. The mimosine-induced expression of Drg-1 was mainly attributable to increased transcription likely by the c-Jun/AP-1 transcription factor. Because induction of Drg-1 is an early event after mimosine treatment and is observed before a notable reduction in the steady-state level of mature eIF5A, eIF5A does not appear to be involved in the modulation of Drg-1 expression.

The retinoblastoma gene and its product are targeted by ICBP90: a key mechanism in the G1/S transition during the cell cycle

The retinoblastoma protein (pRB) is encoded by the RB1 gene whose promoter contains several putative binding sites for ICBP90 (Inverted CCAAT box Binding Protein of 90 kDa), a transcriptional regulator of the topoisomerase IIalpha gene. ICBP90 has two consensus binding sites for pRB in its primary sequence. Here, we show that pRB and ICBP90 co-immunoprecipitate in cell extracts of proliferating human lung fibroblasts and of proliferating or confluent Jurkat cells. GST pull-down assays and immunocytochemistry, after cell synchronization in late G1 phase, confirmed this interaction. Overexpression of ICBP90 induces downregulation of pRB expression in lung fibroblasts as a result of mRNA decrease. DNA chromatin immunoprecipitation experiment shows that ICBP90 binds to the RB1 gene promoter under its methylated status. Overexpression of ICBP90 increases the S and G2/M phase cell fractions of serum-starved lung fibroblasts as assessed by flow cytometry analysis and increases topoisomerase IIalpha expression. Together, these results show that ICBP90 regulates pRB at the protein and gene transcription levels, thus favoring the entry into the S phase of the cells. We propose that ICBP90 overexpression, found in cancer cells, is involved in the altered checkpoint controls occurring in cancerogenesis.

Transcriptional Blockade Induces p53-dependent Apoptosis Associated with Translocation of p53 to Mitochondria

The tumor suppressor p53 functions as a transcriptional activator to induce cell cycle arrest and apoptosis in response to DNA damage. Although p53 was also shown to mediate apoptosis in a manner independent of its transactivation activity, the mechanism and conditions that trigger such cell death have remained largely unknown. We have now shown that inhibition of RNA polymerase II-mediated transcription by alpha-amanitin or RNA interference induced p53-dependent apoptosis. Inhibition of pol II-mediated transcription resulted in down-regulation of p21Cip1, which was caused by both transcriptional suppression and protein degradation, despite eliciting p53 accumulation, allowing the cells to progress into S phase and then to undergo apoptosis. This cell death did not require the transcription of p53 target genes and was preceded by translocation of the accumulated p53 to mitochondria. Our data thus suggested that blockade of pol II-mediated transcription induced p53 accumulation in mitochondria and was the critical factor for eliciting p53-dependent but transcription-independent apoptosis.

P-glycoprotein expression is induced in human pancreatic cancer xenografts during treatment with a cell cycle regulator, mimosine

Application of several cell cycle checkpoint regulators seem to be promising in various experimental models including pancreatic cancer, and they are being evaluated in Phase I-II clinical trials. Among these compounds, mimosine, a plant-derived amino acid has shown an antineoplastic effect on human lung or pancreatic cancer xenografts in addition to cell cycle arrest in the late G1 phase. In the present study, immunosuppressed CBA mice bearing subcutaneously growing human ductal pancreatic adenocarcinomas were treated with 30 mg/kg L-mimosine for 34 days. The treatment resulted in retardation of tumor growth, accompanied by a significantly diminished proliferative activity (22.6%+/-1.7% Ki-67 positivity vs. 29.9%+/-1.1% in controls, mean+/-SEM, P<0.007) and an increased apoptotic rate (14.5+/-1.1 apoptotic cells/mm2 vs. 3.8+/-0.4/mm2 in the controls, P<0.0001). The immunohistochemical expression of the multidrug resistance gene (MDR1)-encoded P glycoprotein (p 170) was studied. The parental and the untreated tumors did not express p 170 protein, but in the mimosine-treated samples 30 to 60% of the carcinoma cells displayed a linear, membrane bound positivity. The results indicate that P-glycoprotein is inducible by a cell cycle regulator, creating an acquired resistant phenotype.

Antidermatophytic and bacterial activity of mimosine

Mimosine, a non-protein aromatic amino acid was tested at 100, 50 and 25 microg/mL on some human pathogenic bacteria and fungi. Mimosine exhibited total lethality towards Trichophyton tonsurans and Trichophyton rubrum at 100 microg/mL. Among the tested bacteria Staphylococcus aureus was inhibited to a larger extent than the other bacteria. The studies revealed mimosine to be potent against fungi rather than bacteria. This study reports the effect of mimosine on dermatophytes for the first time.

Mimosine attenuates serine hydroxymethyltransferase transcription by chelating zinc. Implications for inhibition of DNA replication

L-mimosine is a naturally occurring plant amino acid and iron chelator that arrests the cell cycle in the late G(1) phase, although its mechanism of action is not known. Some studies indicate that mimosine prevents the initiation of DNA replication, whereas other studies indicate that mimosine disrupts elongation of the replication fork by impairing deoxyribonucleotide synthesis by inhibiting the activity of the iron-dependent enzyme ribonucleotide reductase and the transcription of the cytoplasmic serine hydroxymethyltransferase gene (SHMT1). In this study, the mechanism for mimosine-induced inhibition of SHMT1 transcription was elucidated. A mimosine-responsive transcriptional element was localized within the first 50 base pairs of the human SHMT1 promoter by deletion analyses and gel mobility shift assays. The 50-base-pair sequence contains a consensus zinc-sensing metal regulatory element (MRE) at position -44 to -38, and mutation of the MRE attenuated mimosine-induced transcription repression. Mimosine treatment eliminated MRE- and Sp1-binding activity in nuclear extracts from MCF-7 cells but not in nuclear extracts from a mimosine-resistant cell line, MCF-7/2a. MCF-7 cells cultured in zinc-depleted medium for more than 16 days were viable and lacked cytoplasmic serine hydroxymethyltransferase protein, confirming that mimosine inhibits SHMT1 transcription by chelating zinc. The disruption of DNA-protein interactions by zinc chelation provides a general mechanism for the inhibitory effects of mimosine on nuclear processes, including replication and transcription. Furthermore, this study establishes that SHMT1 is a zinc-inducible gene, which provides the first mechanism for the regulation of folate-mediated one-carbon metabolism by zinc.

Canonical Wnt activity regulates trunk neural crest delamination linking BMP/noggin signaling with G1/S transition

Delamination of premigratory neural crest cells depends on a balance between BMP/noggin and on successful G1/S transition. Here, we report that BMP regulates G1/S transition and consequent crest delamination through canonical Wnt signaling. Noggin overexpression inhibits G1/S transition and blocking G1/S abrogates BMP-induced delamination; moreover, transcription of Wnt1 is stimulated by BMP and by the developing somites, which concomitantly inhibit noggin production. Interfering with β-catenin and LEF/TCF inhibits G1/S transition, neural crest delamination and transcription of various BMP-dependent genes, which include Cad6B, Pax3 and Msx1, but not that of Slug,Sox9 or FoxD3. Hence, we propose that developing somites inhibit noggin transcription in the dorsal tube, resulting in activation of BMP and consequent Wnt1 production. Canonical Wnt signaling in turn stimulates G1/S transition and generation of neural crest cell motility independently of its proposed role in earlier neural crest specification.

A genotoxic screen: rapid analysis of cellular dose-response to a wide range of agents that either damage DNA or alter genome maintenance pathways

SNP analysis has come to the forefront of genomics since the mouse and human genomes have been sequenced. High throughput functional screens are necessary to evaluate these sequence databases. Described here is a genotoxic screen: a rapid method that determines the cellular dose-response to a wide range of agents that either damage DNA or alter basic cellular pathways important for maintaining genomic integrity. Importantly, a single person utilizing standard tissue culture equipment may perform these assays composed of 20 agents that attack genomic integrity or maintenance at many different levels. Thus, a small lab may perform this screen to determine the integrity of a wide range of DNA repair, chromatin metabolism, and response pathways without the limitations of investigator bias. A genotoxic screen will be useful when analyzing cells with either known genetic alterations (generated directly by the investigator or derived from individuals with known mutations) or unknown genetic alterations (cells with spontaneous mutations such as cancer-derived cells). Screening many genotoxins at one time will aid in determining the biological importance of these altered genes. Here we show the dose-response curves of mouse embryonic stem (ES) cells and HeLa cells exposed to 20 genotoxic agents. ES cells were chosen since they are amenable to genetic alteration by the investigator. HeLa cells were chosen since they were derived from cancer and are commonly used. Comparing the dose-response curves of these two cell lines show their relative sensitivity to these agents and helps define their genotoxic profile. As a part of phenomics, a large genotoxic profile database for cancer-derived cells, when integrated with other databases such as expression profiles and comparative genomic hybridization, may aid in maximizing the effectiveness of developing anti-cancer protocols.

Cyclin dependent kinase inhibitor p27(Kip1) is upregulated by hypoxia via an ARNT dependent pathway

Expression of cyclin dependent kinase (Cdk) inhibitor p27(Kip1), which blocks cell cycle progression from G(1) to S phase, can be regulated via multiple mechanisms including transcription, protein degradation, and translation. Recently, it was shown that p27(Kip1) plays an important role in the cellular response to hypoxia. However, the mechanisms involved in the hypoxia-induced regulation of p27(Kip1) expression are still not clear. In this study, we compare the expression of p27(Kip1) in two related murine hepatoma cell lines, Hepa-1 and c4. Hepa-1 produces functional aryl hydrocarbon receptor nuclear translocator (ARNT). c4 cells are derived from Hepa-1, but are ARNT deficient. Interestingly, we observed cell line-dependent effects of hypoxia on the expression of p27(Kip1). The level of p27(Kip1) protein in Hepa-1 cells is enhanced by hypoxia, but is reduced by hypoxia in c4 cells. Further investigation demonstrated that hypoxia-induced, ARNT-mediated, transactivation of the p27(Kip1) gene in Hepa-1 cells is responsible for the increase in p27(Kip1) protein. Once c4 cells were stably transfected with the wild type ARNT gene, a hypoxia-induced increase in p27(Kip1) mRNA was observed and reduction of p27(Kip1) protein caused by hypoxia was blocked. Hence, our data indicate that ARNT is involved in transcriptional upregulation of the p27(Kip1) gene under hypoxic conditions.

Potential therapeutic applications of some antinutritional plant secondary metabolites

Plant-based formulations have been used since ancient times as remedial measures against various human and animal ailments. Over the past 20 years interest in traditional medicines has increased considerably in many parts of the world. Whereas modifications in lifestyles, including diet, have had a profound effect on the increased risks of various diseases, there is considerable scientific evidence, both epidemiological and experimental, regarding vegetables and fruits as key features of diets associated with reduced risks of diseases such as cancers and infections. This has led to the use of a number of phytometabolites as anticarcinogenic and cardioprotective agents, promoting a dramatic increase in their consumption as dietary supplements. There are changing perceptions regarding the therapeutic potential of various plant secondary metabolites (PSMs), some of which have also been known to possess certain antinutritional qualities. The knowledge gained at the cellular and molecular levels, and biological activities of PSMs including tannin-polyphenols, saponins, mimosine, flavonoids, terpenoids, and phytates, would be useful in planning for future epidemiological studies and human cancer prevention trials, especially when a large pure dosage is not the option to deliver the active compounds to many tissues. It is well observed that alteration of cell cycle regulatory gene expression is frequently found in tumor tissues or cancer cell lines, and studies have suggested that the herbal-based or plant-originated cell cycle regulators might represent a new set of potential targets for anticancer drugs. The recent upsurge of interest in this area of research and advances made therein indicate that the impact of a number of diseases affecting humans and animals may be lessened, if not prevented, by simple dietary intake of PSMs with putative therapeutic properties.

EIF3 p170, a mediator of mimosine effect on protein synthesis and cell cycle progression

l-Mimosine, a plant amino acid, can reversibly block mammalian cells at late G1 phase and has been suggested to affect translation of mRNAs such as p27, the CDK inhibitor. However, the mechanism of this effect is not known. Regulation of translation generally occurs at the initiation step that, in mammalian cells, is a complex process that requires multiple eukaryotic initiation factors (eIFs) and ribosome. The effects of mimosine on initiation factors or regulators consequently will influence translation initiation. P170, a putative subunit of eIF3, has been suggested to be nonessential for eIF3 function to form preinitiation complexes and it may function as a regulator for translation of a subset of mRNAs. In this article, we tested this hypothesis and investigated whether eIF3 p170 mediates mimosine effect on mRNA translation. We found that p170 translation was dramatically reduced by mimosine due to its iron-chelating function. The decreased expression of p170 by mimosine caused diminished de novo synthesis of tyrosinated alpha-tubulin and elevated translation of p27 before cell cycle arrest. These observations suggest that p170 is likely an early response gene to mimosine treatment and a mediator for mimosine effect on mRNA translation. The effect of p170 on the synthesis of tyrosinated alpha-tubulin and p27 in a reciprocal manner also suggests that p170 functions as a regulator for mRNA translation.

Cell cycle arrest by Kaposi's sarcoma-associated herpesvirus replication-associated protein is mediated at both the transcriptional and posttranslational levels by binding to CCAAT/enhancer-binding protein alpha and p21(CIP-1)

Lytic-cycle replication of Kaposi's sarcoma-associated herpesvirus (KSHV) in PEL cells causes G(1) cell cycle arrest mediated by the virus-encoded replication-associated protein (RAP) (or K8 protein), which induces high-level expression of the cellular C/EBPalpha and p21 proteins. Here we have examined the mechanism of this induction at both the transcriptional and posttranslational levels. RAP proved to bind very efficiently to both C/EBPalpha and p21 and stabilized them by up to 10-fold from proteasome-mediated degradation in vitro. Cross-linking revealed that RAP itself forms stable dimers and tetramers in solution and forms higher-order complexes but not heterodimers with C/EBPalpha. Cotransfection of RAP with C/EBPalpha cooperatively stimulated both the C/EBPalpha and p21 promoters in luciferase reporter gene assays. Only the basic/leucine zipper region of RAP was needed for interaction with and stabilization of C/EBPalpha, but both the N-terminal and C-terminal domains were required for transcriptional augmentation. In vitro-translated RAP interfered with DNA binding by C/EBPalpha in electrophonetic mobility shift assay (EMSA) experiments but did not itself bind to the target C/EBPalpha sites or form supershifted bands. However, in endogenous chromatin immunoprecipitation (ChIP) assays with tetradecanoyl phorbol acetate-induced PEL cells, RAP proved to specifically associate with the C/EBPalpha promoter in vivo, but only in a C/EBPalpha-dependent manner, implying an in vivo piggyback interaction with DNA-bound C/EBPalpha. Expression of exogenous RAP (Ad-RAP) caused G(1)/S cell cycle arrest in human dermal microvascular endothelial cells and also induced both the C/EBPalpha and p21 proteins, which formed punctate nuclear patterns that colocalized with RAP in PML nuclear bodies. In the presence of RAP, C/EBPalpha was also efficiently recruited into viral DNA replication compartments in both infected and cotransfected cells. In support of a direct role for this interaction in viral DNA replication, three C/EBPalpha binding sites were identified by in vitro EMSA experiments within a 220-bp core segment of the duplicated KSHV Ori-Lyt region, and although RAP did not bind to Ori-Lyt DNA directly in vitro, both endogenous RAP and C/EBPalpha were found to be associated with the Ori-Lyt region by ChIP assays in lytically induced PEL cells. Finally, we found that the KSHV lytic cycle could not be triggered by either synchronizing KSHV latently infected PEL cells in G(1) phase or inducing p21 in a C/EBPalpha-independent process.

ICBP90 belongs to a new family of proteins with an expression that is deregulated in cancer cells

ICBP90 (Inverted CCAAT box Binding Protein of 90 kDa) is a recently identified nuclear protein that binds to one of the inverted CCAAT boxes of the topoisomerase IIalpha (TopoIIalpha) gene promoter. Here, we show that ICBP90 shares structural homology with several other proteins, including Np95, the human and mouse NIRF, suggesting the emergence of a new family of nuclear proteins. Towards elucidating the functions of this family, we analysed the expression of ICBP90 in various cancer or noncancer cell lines and in normal or breast carcinoma tissues. We found that cancer cell lines express higher levels of ICBP90 and TopoIIalpha than noncancer cell lines. By using cell-cycle phase-blocking drugs, we show that in primary cultured human lung fibroblasts, ICBP90 expression peaks at late G1 and during G2/M phases. In contrast, cancer cell lines such as HeLa, Jurkat and A549 show constant ICBP90 expression throughout the entire cell cycle. The effect of overexpression of E2F-1 is more efficient on ICBP90 and TopoIIalpha expression in noncancer cells (IMR90, WI38) than in cancer cells (U2OS, SaOs). Together, these results show that ICBP90 expression is altered in cancer cell lines and is upregulated by E2F-1 overexpression with an efficiency depending on the cancer status of the cell line.

Cell cycle inhibition mediated by the outer surface of the C/EBPalpha basic region is required but not sufficient for granulopoiesis

CCAAT/enhancer binding protein alpha (C/EBPalpha) transactivates target genes dependent upon DNA binding via its basic region-leucine zipper domain and slows G1 progression by interaction with E2F, cdk2, or cdk4. E2F interacts with the non-DNA-binding surface of the C/EBPalpha basic region and C/EBPalpha residues 1-70 are required for repressing E2F targets, while cdk2 and cdk4 bind residues 177-191. C/EBPalpha-ER induces the 32D cl3 myeloblast cell line to differentiate to granulocytes. C/EBPalpha-ER variants incapable of binding DNA slowed G1, but did not induce early or late granulopoiesis, indicating that cell cycle inhibition as mediated by C/EBPalpha is not sufficient for differentiation. C/EBPalpha-ER variants lacking residues 11-70 or residues 11-70 and 178-200 both slowed the G1 to S transition. C/EBPalpha(GZ)-ER, containing the GCN4 rather than the C/EBPalpha leucine zipper, also slowed G1. In contrast, C/EBPalpha(BRM2)-ER, carrying mutations in the outer surface of the basic region required for interaction with E2F, did not slow G1. C/EBPalpha(BRM2)-ER induced early markers of granulopoiesis much less efficiently than C/EBPalpha-ER and did not direct terminal maturation. Inhibition of G1 progression using mimosine increased induction of late markers by G-CSF. Thus, both DNA binding and cell cycle arrest, mediated by opposite surfaces of the C/EBPalpha basic region, are required for granulopoiesis.

Mimosine, the Allelochemical from the leguminous tree Leucaena leucocephala, selectively enhances cell proliferation in dinoflagellates

Mimosine, the allelochemical from the leguminous tree Leucaena leucocephala, is toxic to most terrestrial animals and plants. We report here that while mimosine inhibits major phytoplankton groups, it enhances cell proliferation in dinoflagellates. On addition to coastal seawater samples, mimosine is able to confer a growth advantage to dinoflagellates. The use of mimosine will promote the isolation and culture of this group of phytoplankton.

Association between the cell cycle and neural crest delamination through specific regulation of G1/S transition

Delamination of premigratory neural crest cells from the dorsal neural tube depends both upon environmental signals and cell-intrinsic mechanisms and is a prerequisite for cells to engage in migration. Here we show that avian neural crest cells synchronously emigrate from the neural tube in the S phase of the cell cycle. Furthermore, specific inhibition of the transition from G1 to S both in ovo and in explants blocks delamination, whereas arrest at the S or G2 phases has no immediate effect. Thus, the events taking place during G1 that control the transition from G1 to S are necessary for the epithelial to mesenchymal conversion of crest precursors.

The antifungal drug ciclopirox inhibits deoxyhypusine and proline hydroxylation, endothelial cell growth and angiogenesis in vitro

The hypusine biosynthetic steps represent novel targets for intervention in cell proliferation. Hypusine is a rare amino acid, formed posttranslationally in one cellular protein, eIF5A, and is essential for cell proliferation. Deoxyhypusine hydroxylase, the metalloenzyme catalyzing the final step in hypusine biosynthesis, and prolyl 4-hydroxylase, a non-heme iron enzyme critical for collagen processing, can be inhibited by small chelating molecules that target their essential metal atom. We examined the effects of 5 compounds (ciclopirox, deferiprone, deferoxamine, mimosine and 2,2'-dipyridyl) on these protein hydroxylases in HUVECs, on cell proliferation and on angiogenesis using 2 model assays: tube-like vessel formation on Matrigel and the chick aortic arch sprouting assay. These compounds inhibited cellular deoxyhypusine hydroxylase in a concentration-dependent manner, but their efficacy varied widely in the following order: ciclopirox--> deferoxamine-->2,2'-dipyridyl-->deferiprone-->mimosine (IC(50) 5-200 microM). Inhibition of DNA synthesis, following the same order (IC(50) 10-450 microM), correlated with G(1) arrest of the cell cycle. These compounds also inhibited proline hydroxylation and maturation of collagen in HUVECs and caused inhibition of angiogenesis in vitro. Of the compounds tested, ciclopirox was by far the most effective inhibitor of HUVEC proliferation and angiogenesis. The strong antiangiogenic activity of this readily available antifungal drug along with its antiproliferative effects suggests a new potential application for ciclopirox in the treatment of solid tumors.

Inhibition of ultraviolet B (UVB) induced apoptosis in A431 cells by mimosine is not dependent on cell cycle arrest

Ultraviolet (UV) radiation is a strong apoptotic trigger in many cell types. We have previously reported that a plant amino acid, mimosine (beta [N-(3-hydroxy-4-pyridone)]-alpha-aminopropionic acid), with a well-known reversible G1 cell cycle arrest activity can inhibit apoptosis induced by UV irradiation and RNA polymerase II blockage in human A431 cells. Here, apoptosis was measured with a fluorimetric caspase activation assay. Interestingly, the protective state was effective up to 24 h following removal of mimosine from the culture medium while cells were progressing in the cell cycle. Our results demonstrate that the protective effect of mimosine against UV-induced apoptosis can be dissociated from its G1 cell-cycle arrest activity.

Tuning up or down the UV-induced apoptosis in Chinese hamster ovary cells with cell cycle inhibitors

Exposure to UVC induces apoptosis in Chinese hamster ovary (CHO.K1) cells. While studying the underlying mechanism, we found that a variety of cell cycle inhibitors, including colcemid, hydroxyurea and mimosine, enhance the UV-induced apoptosis in these cells. Such enhancement was not dependent on the cell cycle progression nor was it related to the difference in UV sensitivity at different phases of the cell cycle. The expression of p21(waf1/cip1), a general cyclin-dependent kinase (CDK) inhibitor, was deficient in CHO.K1 cells. Ectopic overexpression of the human p21 markedly increased the survival rates of the UV-irradiated cells in the presence of colcemid. In addition, roscovitine, a small-molecule inhibitor of CDK, also inhibited the UV-induced apoptosis. These observations suggest that deregulation of CDK activity may be critical in the UV-induced apoptosis in CHO.K1 cells.

Modulation of intrinsic P-glycoprotein expression in multicellular prostate tumor spheroids by cell cycle inhibitors

The effects of cell cycle inhibition on the expression of the multidrug resistance transporter P-glycoprotein (P-gp) as well as of the cyclin-dependent kinase (CDK) inhibitors p27(Kip1) and p21(WAF-1) were investigated in DU-145 prostate tumor spheroids. With increasing spheroid size the number of cells in the G0/G1 phase augmented, whereas the number of cells in the G2/M phase and the S phase of the cell cycle declined. The number of G0/G1 cells was elevated after incubation with either mimosine, staurosporine or serum-free medium. Mitomycin C and roscovitine increased the number of S phase cells. Roscovitine additionally increased cells in the G2/M phase. Incubation in serum-free medium upregulated p21(WAF-1), p27(Kip1) and P-gp. Mimosine treatment resulted in upregulation of p27(Kip1) and P-gp, whereas p21(WAF-1) remained unchanged. Upon roscovitine treatment p27(Kip1) and p21(WAF-1) were downregulated, whereas P-gp was unaltered. Mitomycin C treatment resulted in downregulation of p27(Kip1) and p21(WAF-1); no significant change in P-gp levels was observed. Staurosporine induced upregulation of p21(WAF-1) whereas p27(Kip1) remained unaltered. P-gp was downregulated upon staurosporine treatment, which was owing to an elevation of intracellular reactive oxygen species by this compound. It is concluded that upregulation of P-gp in G0/G1 phase cells requires coexpression of the CDK inhibitor p27(Kip1) but not the CDK inhibitor p21(WAF-1).

p27(Kip1) enhances myelin basic protein gene promoter activity

The process of oligodendrocyte differentiation is a complex event that requires cell cycle withdrawal, followed by the activation of a specific transcriptional program responsible for the synthesis of myelin genes. Because growth arrest precedes differentiation, we sought to investigate the role of cell cycle molecules in the activation of myelin gene promoters. We hypothesized that the cell cycle inhibitor p27(Kip1), which is primarily responsible for arresting proliferating oligodendrocyte progenitors, may be involved in the transcriptional regulation of myelin genes. In agreement with this hypothesis, overexpression of p27(Kip1) in the CG4 cell line, but not in 3T3 fibroblasts, enhances the expression of luciferase driven by the myelin basic protein (MBP) promoter. Interestingly, this effect is specific for p27(Kip1); overexpression of other cell cycle inhibitors had no effect. Additionally, this effect is independent of halting the cell cycle; treatment with the cell cycle blocker roscovitine did not affect MBP promoter usage. We conclude that p27(Kip1) contributes to oligodendrocyte differentiation by regulating transcription of the MBP gene.